On the fourth day, venture into the national parks surrounding Nga Bay. Visit the Ao Phang Nga National Park, known for its dramatic limestone karsts rising from emerald-green waters. Take a guided kayak tour through the mangrove forests, explore hidden caves, and marvel at the unique rock formations. Don't miss the chance to visit the Khao Sok National Park, home to one of the oldest rainforests in the world. Embark on a jungle trek, spot wildlife, and take a refreshing dip in the natural pools and waterfalls.